1. Field Of The Invention
This invention relates to the reduction in magnitude of radiated noise emanating from clocked digital circuitry and more pailing itself, whose frequency spectral components have been spread for the purpose of noise reduction.
2. Description of the Prior Art
Modern digital equipment is generally controlled by microprocessors or similar clocked control circuitry which are, in turn, tied to a master clock. It is the synchronization of the various digital events to a master clock that causes the emanation of electromagnetic radiation at frequencies which are harmonically and subharmonically related to the master clock frequency. These radiated spectral components can interfere with radio and navigation equipment. An example of this type of interference is the use of portable lap-top computers aboard commercial aircraft where sensitive radio navigation equipment can be disturbed.
In the Brown patent, U.S. Pat. No. 5,115,202, a binary pseudo-random (PN) sequence was substituted for a conventional digital clock circuit in a chopper stabilized amplifier. This resulted in the reduction of interference which was caused by the presence of a digital clock signal in the amplifier. While the direct substitution of a PN spreading sequence in place of the digital clock solved the interference problem for signals below the clock frequency, we should note that the state transitions of the PN sequence are still aligned with the master clock. Another solution is required for reduction of high frequency spectral components related to the clock frequency.